The shift to mobile is happening as Google’s biggest, most
lucrative business — desktop search — is slowing. The share of
clicks on Google
results that happen on desktop computers has fallen to 73 percent
from 77 percent in the last six months, while the share of clicks
on tablets and smartphones has increased to 27 percent from 23
percent, according to data from Adobe.

The problem is that clicks on retail ads on tablets, for
instance, cost about 16 percent less than they do on the
desktop, according to
Adobe. The price of clicks on retail ads on tablets rose 16
percent over the last year, but on smartphones they fell 11
percent.